Slot scanners are often used to read and decode bar codes which are disposed on various items. An example of a slot scanner is shown in U.S. Pat. No. 5,717,195, incorporated herein by reference. Two-window slot scanners essentially have a horizontal window and a vertical or generally vertical (referred to as “vertical” hereinafter) window on two surfaces of a generally L-shaped housing. Projecting generally upward out of the horizontal window is a light beam that creates a first set of scan lines while projecting generally horizontally out of the vertical window is a light beam that creates a second set of scan lines. When the scanner is in use, an operator (such as a person working at a supermarket checkout counter) moves an object with a bar code over the horizontal window and past the vertical window. If the bar code is located on the bottom of the object, the bar code reflects the light beam projecting out of the horizontal window. If the bar code is located on the side of the object facing the vertical window, the bar code reflects the light beam projecting out of the vertical window.
Attempts have been made to extend the reading ability of scanners beyond the bottom and one side of an object. One way to accomplish this, for example, is to have a light beam projecting out of the horizontal window at an angle, so that a bar code on some other sides of an object not facing the vertical window can be read. A light beam projecting out from near the top of the vertical window, but at a downward angle, may provide some ability to read a bar code located on the top of an object.
Heretofore, two-window scanners have used beam splitters to split a light beam from a single light source, such as a laser, into two beams. The two beams are directed at different sides of a spinning polygon mirror, which reflects the two beams toward arrays of stationary mirrors. A typical polygon mirror used in this fashion is mounted directly on a motor shaft and has three or four reflecting facets. The arrays of stationary mirrors provide paths for the two beams to form two scan patterns.
Use of a single light source with a beam splitter has several disadvantages. One disadvantage is that a single light source, such as a laser, must be powerful enough to provide two light beams of adequate intensity and therefore must operate at a higher power, which results in a shorter expected operating life. Another disadvantage is that use of a single light source with a beam splitter may be more costly to manufacture than use of two light sources with no beam splitter. This is because a system using beam splitters usually needs additional mirrors and alignment adjustments that actually are more expensive than having two light sources. Yet another disadvantage of using a single light source is that once that light source fails, the scanner becomes non-operational until the light source is replaced.